code: def test_UpdateFeatures(self) -> None:
      parameters = {"x": 0, "y": "a"}
      new_parameters = {"z": "foo"}
  
      # pyre-fixme[6]: For 1st param expected `Dict[str, Union[None, bool, float,
      #  int, str]]` but got `Dict[str, Union[int, str]]`.
      # pyre-fixme[6]: For 2nd param expected `Optional[int64]` but got `int`.
      obsf = ObservationFeatures(parameters=parameters, trial_index=3)
  
      # Ensure None trial_index doesn't override existing value
      obsf.update_features(ObservationFeatures(parameters={}))
      self.assertEqual(obsf.trial_index, 3)
  
      # Test override
      new_obsf = ObservationFeatures(
          # pyre-fixme[6]: For 1st param expected `Dict[str, Union[None, bool,
          #  float, int, str]]` but got `Dict[str, str]`.
          parameters=new_parameters,
          trial_index=4,
          start_time=pd.Timestamp("2005-02-25"),
          end_time=pd.Timestamp("2005-02-26"),
          random_split=7,
      )
      obsf.update_features(new_obsf)
      self.assertEqual(
          obsf.parameters, {**parameters, **new_parameters}
      )
      self.assertEqual(obsf.trial_index, 4)
      self.assertEqual(obsf.random_split, 7)
      self.assertEqual(obsf.start_time, pd.Timestamp("2005-02-25"))
      self.assertEqual(obsf.end_time, pd.Timestamp("2005-02-26"))
  
imports: import json
  from unittest.mock import Mock, PropertyMock
  import numpy
  import pandas
  from ax.core.arm import Arm
  from ax.core.base_trial import TrialStatus
  from ax.core.batch_trial import BatchTrial
  from ax.core.data import Data
  from ax.core.generator_run import GeneratorRun
  from ax.core.map_data import MapData, MapKeyInfo
  from ax.core.observation import Observation, ObservationData, ObservationFeatures, observations_from_data, observations_from_map_data, recombine_observations, separate_observations
  from ax.core.trial import Trial
  from ax.utils.common.testutils import TestCase
label_desc: Use image node_id 4 for calling the ObservationsTest obj's underlying member method code with example usage: obj.test_UpdateFeatures() without return types